Low power portable equipment is often designed to be powered by small dry cells that are not designed to be recharged. In everyday life, such disposable chemical voltage sources are called batteries. Batteries of standard sizes AA and AAA are popular. These letters indicate the external format of the battery. The internal structure can be completely different. In this form factor, various types of batteries are produced, including rechargeable (accumulators).
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What is a battery
The term "battery" is not entirely correct. A battery is a power source made up of several elements. So, a full-fledged battery can be called a 3R12 (3LR12) element - a “square battery” (336 according to the Soviet classification) - made up of three elements.Also, the battery consists of 6 cells of the element 6R61 (6LR61) - "Krona", "Korund". But the name "battery" in everyday life is also applied to single-element chemical power sources, including AA and AAA sizes. In English terminology, a single element is called Cell, and a battery of two or more voltage sources is called Battery.
Such elements are hermetically sealed cylindrical vessels. They undergo transformation chemical energy into electrical. The reagents (oxidizing agent and reducing agent) that create the EMF are placed in a glass of zinc or steel. The bottom of the glass serves as a negative terminal. Previously, the entire outer surface of the glass was given under the negative pole, but this path led to frequent short circuits. In addition, the surface of the cylinder was exposed to corrosion, which led to a reduction in the service life and storage of the element. In modern batteries, a coating is applied to the outside to protect against corrosion and serve as insulation against short circuits. The current collector of the positive pole is a graphite rod, which is brought out.
Types of batteries
Batteries are classified into categories according to different criteria. The main one should be recognized as the chemical composition - the technology for obtaining EMF. For practical use, there are several more different characteristics.
By chemical composition
The potential difference at the poles of galvanic cells is created due to the chemical reaction between substances in the electrolyte solution and stops when the ingredients have completely reacted. You can achieve the necessary processes in different ways. According to this criterion, batteries are divided into:
- Salt. The traditional type of batteries, invented about 100 years ago.The reaction between zinc and manganese dioxide occurs in an electrolyte medium - a thickened ammonium salt solution. Along with low weight and low price, these elements have a number of significant disadvantages:
- small load capacity;
- tendency to self-discharge during storage;
- poor performance at low temperatures.
The production technology is considered obsolete, therefore, such elements on the market of galvanic cells are forced out by new types.
- Alkaline (alkaline) elements are considered more modern. They are arranged in the same way, but the electrolyte is an alkali solution (potassium hydroxide). These batteries have advantages over saline ones:
- large capacity and load capacity;
- low self-discharge current determines long shelf life;
- good performance at low temperatures.
You have to pay for this with a lot of weight and an increased price.
- The most advanced cells at present are lithium (not to be confused with lithium batteries!). As a "plus" reagent, they use lithium, the negative one can be different. Various liquids are also used as an electrolyte. This technology allows you to get elements that have the following advantages:
- light weight (less than other types);
- long shelf life due to very low self-discharge;
- increased capacity and load capacity.
On the other side of the scale - the high cost.
According to these three technologies, elements of AA and AAA sizes are produced. It is worth mentioning two other types of batteries:
- mercury;
- silver.
According to these technologies, mainly disk-type batteries are produced.Such elements have their advantages and disadvantages, but the days of mercury batteries are numbered - international agreements suggest a decrease in production volumes and a complete ban on production in the coming years.
By size
The size (more precisely, volume) of a battery uniquely determines its electrical capacity (within the limits of technology) - the more reagents can be placed inside the cylinder, the longer the reaction takes. The capacity of an AA size salt cell will be larger than the capacity of a AAA salt cell. Other form factors of AA batteries are also available:
- A (greater than AA);
- AAAA (less than AAA);
- C - medium length and increased thickness;
- D - increased length and thickness.
These types of elements are not so popular, their scope is limited. Both types are produced only by alkaline and salt technologies.
By rated voltage
The rated voltage of a single cell battery is determined by its chemical composition. Single alkaline, salt galvanic cells at idle give out a voltage of 1.5 V. Lithium power supplies are available both with a voltage of 1.5 V (for compatibility with other types) and with increased voltage (up to 3 V). But in the sizes under consideration, you can only buy one and a half volt elements - to avoid confusion.
For new batteries, the voltage under rated load is close to this value. The more the chemical source is discharged, the more the output voltage sags under load.
Cells can be collected into batteries. Then the output voltage becomes a multiple of the voltage of one element. So, the battery 6R61 ("Krona") contains 6 one and a half volt cells.They give out a total voltage of 9 volts. The size of each cell is small and the capacity of such a battery is low.
What batteries are called finger and little finger
Both of these sizes of galvanic cells belong to the class of finger batteries. This technical term has been used since Soviet times to refer to batteries of a similar shape. The USSR produced single-element salt cells "Uranus M" (316) and alkaline "Quantum" (A316), corresponding to the current type of AA. There were also other cylindrical finger elements of other sizes and proportions.
In the 1990s, merchants in the markets coined the term "little finger" batteries to distinguish AAA cells from other form factors. This name has become widespread in everyday life. But using it in technical materials is at least unprofessional.
Main technical characteristics of AA and AAA batteries
The main difference between AA and AAA finger batteries is size. And he, as already mentioned, determines the capacity.
| Size | Length, mm | Diameter, mm | Electrical capacity, mAh | ||
|---|---|---|---|---|---|
| Lithium | Salt | alkaline | Lithium | ||
| AA | 50 | 14 | 1000 | 1500 | up to 3000 |
| AAA | 44 | 10 | 550 | 750 | 1250 |
It must be remembered that the electrical capacitance depends on the discharge current, and its nominal value for any type of elements does not exceed several tens of milliamps. At currents above 100 mA, the battery capacity will be much lower. This means that a 1000 mAh cell, discharged with a current of 10 mA, will last about 100 hours. But if the discharge current is 200 mA, then the charge will be exhausted much earlier than 5 hours. The capacity will decrease several times. Also, the electrical capacitance of any element will decrease with decreasing temperature.
Depending on the size and technology, batteries have different weights, although this characteristic is rarely decisive - the mass of equipment in most cases significantly exceeds the weight of several batteries. More often it is necessary to know this for the purposes of storage and transportation of galvanic cells.
| Size | Weight, g | ||
|---|---|---|---|
| Salt | alkaline | Lithium | |
| AA | up to 15 | up to 25 | up to 15 |
| AAA | 7-9 | 11-14 | to 10 |
The weight of the batteries has a variation, depending not only on the manufacturing technology, but also on the method of production of the glass. It can be metal with a plastic coating or completely polymer. With three power elements, you can win at best 30 grams of weight. It is unlikely that this can become a determining criterion when choosing.
The shelf life is determined by the self-discharge current and the cell capacity. Self-discharge depends on the technology, capacity depends on the form factor. But in practice, the second characteristic contributes less to charge leakage during storage. At least, this is what the manufacturers assure, indicating approximately the same periods in warehouses for AA and AAA elements. Temperature also affects the shelf life - with its increase, the shelf life decreases.
| Size | Shelf life, years | ||
|---|---|---|---|
| Salt | alkaline | Lithium | |
| AA, AAA | until 3 | up to 5 | 12-15 |
Salt elements have another problem. Batteries of low quality may leak electrolyte. Therefore, the actual shelf life in this case will be even shorter.
Power supplies can be operated in various conditions, including temperature. And the suitability of galvanic cells will be different - also depending on the manufacturing technology. It was mentioned that salt batteries do not work well at temperatures below zero.Lithium, despite all its advantages, has an upper limit of +55 ° C (the lower limit is up to minus 40 (usually up to minus 20), depending on the manufacturer). Alkaline ones have a wide range - from about minus 30 to +60 ° C and are the most versatile in this regard.
Summing up, it should be noted that the AA and AAA families actually include a large number of variations of galvanic cells. You can choose a battery for a wide range of operating conditions and a wide range of costs.
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